1. Field of the Invention
The present invention generally relates to combined plain old telephone systems (POTS) transmissions and digital subscriber line (DSL) transmissions, and more particularly to an apparatus for providing combined POTS and DSL transmissions to a customer premises, while eliminating the need for duplicative POTS filters or the need to undertake extensive premises rewiring.
2. Discussion of the Related Art
Prompted largely by the growth in Internet usage, the provision of xDSL services to customer premises has proliferated over recent years. In this regard, the descriptor xe2x80x9cxxe2x80x9d preceding the DSL designator is used to broadly denote a variety of DSL services, including ADSL, RADSL, HDSL, etc. As is known, xDSL transmissions are sent to customer premises over the same twisted pair cabling as POTS transmission are sent. Since xDSL transmissions are communicated in a frequency band that is separate and distinct from the POTS frequency band, transmitting both types of signals over the same cabling (even at the same time), generally is not a problem. Specifically, the POTS frequency band is defined between approximately DC and approximately 4 kHz, while xDSL frequency bands (although they vary depending upon the specific service) are generally defined by a lower cutoff frequency of approximately 30 kHz, and an upper cutoff frequency that depends upon the particular xDSL service.
However, it is known that some measure of additional protection is generally necessary, when the communications occur simultaneously. In this regard, a person speaking into a telephone handset will generally observe audible noise over the handset, even though the xDSL signals are at frequencies above the audible range. It has been generally determined that this audible noise is a result of circuit components within a telephone handset reacting with the xDSL signals to generate lower frequency noise signals, also called intermodulation products. Therefore, some level of additional protection must be provided in order to satisfactorily transmit both POTS information and xDSL signals at the same time.
This additional protection is usually provided by placing a POTS filter at the customer premises. As the name suggests, a POTS filter is a low pass filter that rejects signals at frequencies higher than the POTS frequency band (thus filtering the POTS band signals). Likewise, most xDSL equipment includes a front-end high-pass filter to reject lower frequency POTS signals (as POTS signals tend to distort the xDSL signals by clipping at the analog to digital converter). In this way, xDSL signals are isolated from the POTS signals, which can then be individually routed to the appropriate locations at the customer premises. There are, however, at least two specific manners in which the POTS filter is provided at the customer premises.
First, the local loop is often tapped at the point of entry into the customer premises, and the POTS filter placed at the point of entry. The output of the POTS filter can then be electrically connected to the wiring entering the premises so that all jacks within the premises receive the protection of the POTS filter. Unfortunately, since dual lines are generally not prewired at a customer premises, the second line carrying the xDSL signals must be routed into the customer premises (which may require drilling through walls or other measures). Sometimes this does not pose a significant problem, particularly when the xDSL line need only be routed to a single location that is relative easy to route the line. However, if access to the xDSL service is desired at multiple locations within the customer premises, then the routing of the signal lines will become more tedious, time consuming, and expensive.
A second, relatively simple solution to implement is to simply provide a POTS filter at every location within the customer premises supporting POTS equipment (e.g., telephones, facsimile machines, PSTN modems, etc.). This filter may be provided in a single housing that simply plugs into the jacks (e.g. RJ-11 jack). Thus, such a filter will need to be provided for every telephone used in the premises. While simple to implement, this solution certainly imposes a significant cost burden on the customer.
Accordingly, an alternative solution that overcomes the shortcomings of the prior art is desired.
Certain objects, advantages and novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the advantages and novel features, the present invention is generally directed to an apparatus that is placed, preferably, at or near the point of entry (or the local loop) of a customer premises. The apparatus operates to do two things. First, it taps off the local loop and passes the tap through a POTS filter. The remainder, which carries the xDSL signal transmissions, is filtered to remove signals within the POTS frequency band and is then frequency shifted upwardly. In addition, the power level of the xDSL transmissions is reduced. In practice, the xDSL signal is terminated at the point of entry of the customer premises, then regenerated at a higher frequency and transmitted at a lower power. Then the tapped signal (which has been passed through the POTS filter) is recombined with the frequency shifted signal, and delivered to the customer premises. In this way, the single line that is routed throughout the customer premises to a plurality of jacks supports both POTS and xDSL transmissions, and no additional filtering need be done.
In accordance with one aspect of the invention, an apparatus is provided for facilitating combined xDSL and POTS communication across a two wire pair. The apparatus includes a first communication port for communication with a central office across a two wire pair, and a second communication port for communication with a customer premises across a two wire pair. A splitter, or tap, is disposed at the first communication port for splitting a combined xDSL and POTS signal into a first and second signal path. A low pass filter is disposed in the first signal path for filtering the xDSL signal from the combined signal in the first signal path, leaving only the low-frequency (POTS frequency) signals. A circuit is disposed in the second signal path that is configured to filter the POTS signal from the combined signal, leaving only the xDSL signal. The circuit is further configured to terminate the xDSL signal and regenerate it at a lower amplitude and higher frequency than the original xDSL signal of the combined signal. Finally, an adder is configured to combine the POTS signal on the first path with the regenerated xDSL signal on the second path, and output the result to the second communication port (for entry into the customer premises).
In accordance with another aspect of the present invention, a method is provided for facilitating combined xDSL and POTS communication across a two wire pair and into a customer premises. In accordance with this aspect of the invention, the method includes the primary steps of receiving a combined signal from a central office, the combined signal having both POTS and xDSL signals, transforming the xDSL signal by shifting it upward in frequency and reducing its amplitude, and directing the transformed signal into the customer premises.